Calculating The Number Of Overwrite Passes For Fmds - Hitachi G1000 User Manual

[(400 × 3) × 2] / 440 = 5.45 = six times
Round up the value (5.45) to the nearest whole number. You need to
overwrite the data six times.
2. Define the shredding settings.
Refer to
data 00 in the text box and add a row to the Data Pattern (User
Setting) list (add rows for performing the shredding operation six
times).
3. Erase the volume data.
Refer to
shredding operation.
4. Repeat steps 2 and 3 using the dummy data FF.
5. Repeat steps 2 and 3 using the dummy data 00.
For more information, see the Top window when selecting Logical Device
section in the Hitachi Virtual Storage Platform G1000 Provisioning Guide for
Open Systems.

Calculating the number of overwrite passes for FMDs

Because of the way space is allocated in FMDs, the dummy data that is used
to overwrite the volume must exceed the capacity of the target volume.
Therefore, before you shred a volume on FMDs, you need to calculate the
number of times the system must overwrite the volume with dummy data.
You must have the Storage Administrator (Provisioning) role to perform this
task.
1. Select an LDEV on the LDEVs tab in the Logical Devices window, and
write down its capacity and the amount of data in the RAID
configuration.
Examples amounts of data in a RAID configuration:
n of RAID5(nxD + 1P)
n of RAID6(nxD + 2P)
2. Use the following formula to calculate the number of times to overwrite
the data (N):
N = (User-capacity-for-Data x 2) / Capacity-of-target-volume
When the capacity of the FMD is 1,600 GB, 1,600GB x n
Example: The capacity of the FMD is 1,600 GB, the RAID configuration is
3D+1P, and the LDEV capacity is 880 GB.
[(1,600 x 3) x 2] / 880 = 10.9 = 11 times
Round up the value (10.9) to the nearest whole number. You need to
overwrite the data 11 times.
You can write dummy data up to eight times in one shredding operation. To
write dummy data nine or more times, perform the shredding operation for
the volume as many times as required.
Hitachi Virtual Storage Platform G1000 Hitachi Volume Shredder User Guide
Defining shredding conditions on page
Defining shredding conditions on page 2-6
Volume Shredder operations
2-6, enter the dummy
and execute the
2–5